High frequency electrical apparatus



Feb. 14. 1956 E. D. MOARTHUR HIGH FREQUENCY ELECTRICAL APPARATUS Filed May 17, 1950 Fi I.

LOAD

Inventor. Elmer D. MC Arthur,

His Attorney United States Patent 2,735,034 HIGH FREQUENCY ELECTRICAL APPARATUS Elmer D. MeArthur, Schenectady, N. Y., assignor' to 4 Claims. (Cl. 315-4) My invention relates to high frequency oscillators and amplifiers and more particularly to such oscillators and amplifiers employing a velocity modulated electron beam.

It is an object of my invention to provide a high frequencyoscillator having an oscillation frequency which is independent of the load on the oscillator.

It'is another object of my invention to" provide a high frequency wide-band amplifier employing a velocity modulated electron beam.

In the attainment of the foregoing objects I provide means for deriving a narrow beam of electrons which travel in a circular path. The electrons in the circularly shaped beam pass a first narrow opening or gap at one end of a conventional wave guide and 180 of rotation later pass a second gap at the opposite end of the guide. As the beam passes the second gap it induces a voltage across it which radiates an electromagnetic wave down the'guide producing an electric field across the first gap. Theelectrons crossing the first gap are velocity modulated according'to the intensity of the electric field across the first gap such that the radius of the circular path traversed by the electrons varies according to this electric field intensity. As the radius of rotation isiin'creased, the electrons pass at a greater distance from the second gap and'induce' a lower voltage across it, wherebythe gap radiates an electromagnetic wave of decreased amplitude down the guide, and a smaller electric field intensity appears across the first gap. As a result of the energy feedback between the first and second gaps "Off the wave guide, an oscillation is set up whose frequencyyis dependent upon the time of travel of theelectroma'gnetic wave between the two gaps. Another wave'guide has at one end a gap which is locatedopposite the'second gap of the feedback wave guide such that the electron beam passes between the two gaps, absorbs energy from the beam and delivers this energy along the guide to a load. Because the separation between the gap in the load wave guide and the gap in the feedback wave guide is relatively large, the coupling between the two guides is very loose, and the load has practically no effect upon the natural frequency of the oscillator.

For additional objects and advantages and for a better understanding of my invention attention is now directed to a following description and accompanying drawing and also to the appended claims in which the features of my invention believed to be novel are particularly pointed out, in which Fig. 1 is a schematic diagram of an oscillator of the type described in this specification and Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1.

Referring to Fig. 1, a resonant wave guide is provided with suitable tuning means such, for example, as a plunger 2 having an adjustable position in the guide. The guide has an airtight window 3, which may be constructed of glass, mica, or some other suitable material, mounted therein. A feedback wave guide 4 is provided with a pair of interaction gaps 5 and 6 at opposite ends. As shown, the g 'p 5- is located Opposite an interaction gap 7 p'rovided'in' one end of guide 1'.

An electron gun structure 8 emits electrons. and .a plurality of focusing wings 9 focus them-into a narrow beam which passes through the space between gaps '5 and 7. Another wave guide 10 is provided at gone end with a narrow gap 11' opposite gap 6 and with an airtight window 12 similar to window '3. The space between windows 3 and 12 and within a semi-circular toroidal envelope 13 is a substantial v'acuum.. A magnetic flux is established between metallic plates'14 whichaare connected to opposite poles of magnetic core 15. Cor-e may be a permanent-magnet as shown or perhaps an electromagnet. This field is perpendicular to the electron beam such that the electrons in thebeam are given a circular path having a radiusthat is proportional to the velocity of the electrons and'to the stre'mgtliof the magnetic field. a

When this device is operated as' a high frequency (iscilla'tor the electrical distance between gaps 5 and 6 is an integral number of-wave' lengths of the operating wave. As the beam of electrons passes gap 6 a' high frequency wave is transmitted along wave guide 4--toward gap 5 and this wave is characterized by an electric Ifield across gap 5 which, as well known-in the art, fringes out be yondthe gap; Because'gap'T is locatednear gap 5 it is tightly coupled thereto-and a. similar electric field appears acro'ss'iti As theb'eamof electrons passes theseggaps' and intercepts [thefringing electric field's, its velocityisaaltered according to the intensity of' the-field and, aslhereinbe'fore'mentioned, changes the velocity of the electrons in the beam which changesith'e radius of curvature of the beam, andthepos'ition of theb'e'arn shifts with respect to gaps 6 and 11. As the distance between the beam. andgap 6varies,-th'eintensity offthe wave"transniitted' along" guide '4 toward gap' '5'-va'ries accordingly, andthe electric fieldproduced'. across gaps 5 and 7 also varies. Thus, thepositionlof'theibeain with respect to gap 6 determines the intensity ofl the electric field across gaps" 5 an'd'7, andthe position-of the beam with respect to gap"6" is dependent upon the intensity of the electric'fields' across gaps 6 and'7. Because .the electrical length of waveguide" 4 between gapsS and 6 is an integral number of wavelengthsof the electromagnetic wave generated" by this oscillator, positive orre enerative feedback is obtained, arid oscillations may be sustainedl Consequently, thebeam moves back and forth between gaps 16 and 11" with -a' lateral displacement which. varies" sinusoidally"withf time, [and the waveradiate'd' by gap 11 along" guide 10 in a sine wave. Gaps 6 and 11 being loosely coupled prevent the load from affecting the oscillator, and a constant frequency is maintained regardless of load changes.

When this device is used as an amplifier, plunger 2 is removed and the high frequency signal to be amplified is introduced through window 3 toward gap 7. If no feedback is desired, gap 6 may be closed olf and as the beam of electrons passes gap 7 and gap 5 it is velocity modulated and induces a field across gap 11 which is dependent upon the wave supplied to gap 7. In the case where this device is to be used as a wide band amplifier, however, the feedback through guide 4 from gap 6 to gap 5 is used in such a way as to extend the passband of the system. By using the arrangement as shown in Fig. 1, less the plunger or tuning member 2, an electrical length between gaps 5 and 6 nearly but not exactly equal to an integral number of wavelengths is chosen.

As an example, let us assume that a carrier wave of wavelength A is to be modulated such that side bands are generated having wavelengths between A and AA, and it is desirable to have uniform response over the band-width A. This may be accomplished in this device by making the physical length of the feedback section "between gapsS and 6 slightly shorter than A but not less than AA. Here, of course, A is a number less than one so that A} is a shorter wavelength than A. Under these circumstances, wavelengths near A?\ will be reinforced by advantage of a constant oscillation frequency which is independent of the load, and when used as a wide band amplifier it can bemade to pass a very wide band at high frequencies with uniform gain.

While this device has been described with reference to'particular embodiments thereof it will be understood that those skilled in the art may make many changes and modifications without departing from the invention.

It is, therefore, with this in mind that I append the following claims to include all such modifications which fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. High frequency electrical apparatus comprising a source of a beam of electrons, a source of magnetic flux located adjacent said electron beam source for producing a magnetic field perpendicular to said beam, said field causing the electrons of said beam to traverse a circular path, a straight hollow conductor provided at opposite ends with a narrow gap and being located diametrically within said beam such that the gaps are adjacent said beam, another hollow conductor having an adjustable length and provided at one end with a narrow gap which is located opposite and near to a first of said gaps in said first hollow conductor, and a third hollow conductor provided at one end with a narrow gap which is located opposite and close to the second of said gaps in said first conductor.

2. In combination of a first hollow conductor being provided at one end with a narrow gap, said conductor being adjustable in length, a second hollow conductor being provided at either end with a narrow gap, one of said gaps being located opposite the gap of said first conductor, a third hollow conductor being provided at one end with a narrow gap, the gap of said third conductor being opposite a gap of said second conductor, a source of free electrons, means for focusing said free electrons into a narrow beam which passes through the opening between said first and second second gaps, magnetic flux producing means located along the path of avsspsa said beam beyond said first and second gaps for causing the path of said electron beam to be circular in shape, said third and fourth gaps being located such that said beam passes between said gaps.

3. A high frequency oscillator comprising a source of electrons, means for focusing said electrons into a narrow beam, a first hollow conductor being provided at one end with a first narrow opening, a second hollow conductor being adjustable in length and being provided with a narrow opening at one end, said narrow openings being close to and opposite each other such that they are tightly coupled, said electron beam being located between said openings, magnetic flux producing means positioned along the path of said beam beyond said narrow openings to provide a magnetic field perpendicular to said beam of electrons, said first conductor being provided at the other end with a second narrow opening located adjacent to said beam, and a third hollow conductor being provided at one end with a narrow opening, which is located opposite said second narrow opening, whereby said beam of electrons is circular and passes said openings between said first and third conductors.

4. A wide band high frequency amplifier comprising a first hollow conductor being provided at opposite ends with a first and second gap, a hollow input conductor being provided at one end with athird gap which is located close to and opposite said first gap, a source of a narrow beam of electrons being located suchthat said beam passes between said first and third gaps, magnetic flux generating means positioned along the path of said beam beyond saidfirst and third gaps to provide a magnetic field which is perpendicular to saidv beam, a second hollow conductor being provided at one end with a fourth gap located at a distance from and opposite to said second gap, said second and fourth gaps being located on opposite sides of the path of said beam whereby electrons of said beam pass therebetween after having passed said first and third gaps, and the dis tance separating said first and second gaps being AX where A is the center wavelength of a signal being amplified and A is the bandwidth desired, whereby an electromagnetic wave introduced into said second conductor is amplified and departs from said third conductor.

References Citedin the tile of this patent UNITED STATES PATENTS 2,272,165

Kusch May 24, 1949 

